Magnetic cascade development device for dry process electrophotography

ABSTRACT

Cascade development device for a dry process electrophotography includes a magnetic endless belt trained around a pair of rollers and a non-magnetic endless roller partially wrapped over the magnetic belt along its going pass and trained around a guide roller spaced apart from the upper one of the pair of rollers and adjacent to the upper end of an development of an electrophotographic recording medium in such a manner that the non-magnetic belt may be separate from the magnetic belt adjacent to the upper one of the pair of rollers. The developer is entrained and transported upon the non-magnetic belt and is freed from the magnetic field when the belts are separated so that the developer may be freely cascaded. Mixing means is provided for mixing the returned developer and guide roller oscillating means is also provided so as to uniformly cascade the developer.

United States Patent Ohta et al.

[451 July25,1972

[54] MAGNETIC CASCADE DEVELOPMENT DEVICE FOR DRY PROCESSELECTROPHOTOGRAPHY [72] Inventors: Wasaburo Ohta, Yokohama; KazuhikoKasuya; Masayuki Yamauchi, both of Kawasaki, all of Japan [73] Assignee:Kabushiki Kaisha Ricoh, Tokyo, Japan [22] Filed: March 13, 1970 21 Appl.No.: 19,360

[30] Foreign Application Priority Data March 15, 1969 Japan ..44/19813[52] U.S.Cl ..ll8/637,l17/17.5

Primary Examiner-Mervin Stein Assistant Examiner-Leo MillsteinAttorney-Burgess, Ryan and Wayne [5 7] ABSTRACT Cascade developmentdevice for a dry process electrophotography includes a magnetic endlessbelt trained around a pair of rollers and a non-magnetic endless rollerpartially wrapped over the magnetic belt along its going pass andtrained around a guide roller spaced apart from the upper one of thepair of rollers and adjacent to the upper end of an development of anelectrophotographic recording medium in such a manner that thenon-magnetic belt may be separate from the magnetic belt adjacent to theupper one of the pair of rollers. The developer is entrained andtransported upon the non-magnetic belt and is freed from the magneticfield when the belts are separated so that the developer may be freelycascaded. Mixing means is provided for mixing the returned developer andguide roller oscillating means is also provided so as to uniformlycascade the developer.

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MAGNETIC CASCADE DEVELOPMENT DEVICE FOR DRY PROCESS ELECTROPIIOTOGRAPHYBACKGROUND OF THE INVENTION The present invention relates to a dryprocess electrophotographic development and more particularly a devicefor cascade development for a dry process electrophotography.

In the conventional cascade development of the type described, adeveloper consisting of a toner, a finely divided pigmented resinouspowder and a carrier of glass beads, etc. is cascaded upon a recordingmedium bearing thereupon a latent electrostatic image so that the tonermay be adhered to the latent electrostatic image, thereby forming avisible powder image. In a typical cascade development device asdisclosed in Japanese Pat. Publication No.16596/1967 (US. Pat.No.3,062,109 to Mayo et al.) a bucket elevator is employed for movingthe developer mixture from a sump region to an area elevated withrespect to the image-bearing surface of a recording medium so as tocascade or pour the developer mixture upon the image-bearing surface. Inthis system, factors affecting the quantity of the developer to besupplied are the shapes, number, velocity, etc. of the buckets whichscoop the developer, so that a number of buckets must be increased orthe conveying velocity must be increased so as to continuously scoopingand cascading the developer, thereby improving the development. Thissystem becomes therefore large in size, complex in construction andexpensive.

SUMMARY OF THE INVENTION It is therefor one object of the presentinvention to provide an improved cascade development system for dryprocess electrophotography which can substantially eliminate the defectsencountered in the conventional system, can be operated in a simplemanner at a less operation cost and can develop a high quality imagehaving no edge effect. The novel feature which is believed to becharacteristic of the present invention lies in the fact that an endlessbelt made of a non-magnetic material (non-magnetic belt) is wrapped overan endless belt made of a magnetic material (magnetic belt) so that thedeveloper mixture consisting of a tonner and a carrier made of amagnetic material such as iron oxides may be attracted upon the surfaceof the non-magnetic belt and continuously entrained so as to be movedupwardly when at least the nonmagnetic belt is driven; and thereafterthe non-magnetic belt is separated from the magnetic belt so that themagnetic force from the magnetic belt will not act upon the developerupon the non-magnetic belt when the developer is cascaded or poured uponthe image-bearing surface of a recording medium.

Opposed to the conventional system, the system in accordance with thepresent invention can continuously and smoothly convey and cascade thedeveloper so that the development can be continuously and smoothlycarried out whereby a high quality image having no edge effect can beproduced.

According to one aspect of the present invention, the nonmagnetic beltis so arranged as to be oscillated when the developer is cascaded uponthe image-bearing surface of the recording medium so that the developermay be uniformly cascaded upon the surface whereby the non-uniformdevelopment due to the insufficient tonner supply can be eliminated.

According to another aspect of the present invention, the developer ismixed after it is dropped or removed away from the recording mediumafter developmentso that the concentration of the tonner and the chargeimparted thereto may be uniformly maintained. Therefore, the developedimage has no developing mark and the supply of the developer is muchfacilitated.

According to another aspect of the present invention, a thinnon-magnetic metallic sheet is used as the non-magnetic belt so that aspecial electrostatic effect is attained, thereby improveing the qualityof developed image.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofillustrative embodiments thereof taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic sectional viewof one embodiment of the present invention;

FIG. 2 A and FIG. 2 B are fragmentary sectional views illustrating theconstruction of the magnetic belts used in the present invention;

FIG. 3 is a diagrammatic sectional view of an electrophotographiccopying machine to which is applied the present invention in one form;and

FIG. 4 is a diagrammatic sectional view illustrating another embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, anelectrostatic latent image formed by the exposure upon a recordingmedium 2 upon a rotary drum 1 rotating in the direction indicated by thearrow is directed toward the developing zone A. The recording medium 2may be a photoconductive material material such as inorganicsemiconductors (for example, selenium, zinc oxide, etc.) and organicsemiconductors (for example, poly-N-vinyl carbazole) applied directlyupon the surface of the rotary drum 1 or an insulatingelectrophotographic copy paper upon which is formed the above describedphotoconductive material in layer. The developing agent 4 in adeveloping agent tray 3 is a dry process developer consisting of theso-called tonner, a pigmented resinous powder, and a carrier made offerromagnetic materials such as powder of iron oxides.

An endless belt 7 incorporating therein a plurality of magnet sectionswhich will be referred to as magnetic belt" hereinafter is trainedaround a driving roller 5 and a driven roller 6 which rotate in thedirection indicated by the arrow b. Another endless belt 9 made of anon-magnetic material such as fabrics, synthetic resins, aluminum, etc.,so that it will be referred to as non-magnetic belt" hereinafter, iswrapped over the magnetic belt 7 and around a guide roller 8.

The developer 4 is adhered to the surface of the non-magnetic belt 9adjacent to the roller 5 and is entrained toward the roller 6. Thenon-magnetic belt 9 is separated from the magnetic belt 7 adjacent tothe roller 6 so that the developer 4 is cascaded or dropped adjacent tothe guide roller 8 upon the recording medium in the developing zone A.The tonner is adhered to the latent electrostatic image upon therecording medium 2 in a manner well known in the art so that a visiblepowder image is developed. Thereafter the developer 4 is returned to thetray 3 and re-circulated in the manner as described hereinbefore. Theexcessively applied tonner is returned to the tray 3 by a fog preventivebrush 10 which may comprise a roller having cotton fabrics, feathers,Japanese paper, etc. affixed thereto and more preferably may comprisesilk fabric folded in the form of a brush with its free ends untwistedas disclosed in Japanese Utility Model Publication No.l2,558/l967.

The developed image is directed toward the transfer zone and after thetransfer of the developed image to a suitable support, the residualtonner upon the recording medium is removed by a cleaning brush 11having the same construction as the brush 10, but being pressed againstthe recording medium 2 with a pressure higher than that of the brush 10.

The magnetic belt 21 shown in FIG. 2-A comprises an endless belt 21amade of fabrics or rubber and a plurality of permanent magnet sectionsaflixed thereto in spaced apart relation with each other. The magnetbelt 21 shown in FIG. 2- B comprises an endless belt 21a and a pluralityof permanent magnet sections 21b incorporated therein. It is notnecessarily required to train the magnetic belt and in one form of thepresent invention it may be in the form of a fixed plate.

FIG. 3 is a diagrammatic sectional view of a photocopying machine towhich is applied the present invention in one form. A seleniumsensitized member is vacuum deposited as a recording medium 32 upon arotary drum 31 rotating in the direction indicated by the arrow 0. Therecording medium 32 is imparted with the positive electrostatic chargeby a charging device 34 to which is applied a high voltage of thousandsof volts from a high voltage source 33 and a light image of an original37 to be reproduced by light sources 35a and 36a is projected through aprojection lens 38 upon the recording medium 32 thereby forming a latentelectrostatic image corresponding to the configuration of the original37 to be reproduced. Reference numerals 33b and 36b designate reflectorsfor the light sources 35a and 36a respectively.

The latent electrostatic image thus formed upon the recording medium 32is directed to the developing zone B. In a developing agent tray 39 iscontained a developer 40 which is entrained upwardly by the cooperationof a magnetic belt 43 trained around a driving roller 41 being a regularpolygon in cross section and a driven roller 42 being also a regularpolygon in cross section and a non-magnetic belt 46 wrapped over themagnetic belt 43 and a guide roller 44 and a tension roller 45 which isbiased by means of a spring 450. The developer 40 is cascaded or droppedadjacent to the guide roller 44 over the developing zone B so that thetonner is adhered to the latent electrostatic image upon the recordingmedium 32, thereby forming a visible powder image. A cover 47 which mayenclose all of the developing device is fixed to the developer tray 39so as to prevent the dispersion of the developer 40 during theoperation.

The guide roller 44 has its shaft 44a fixed to an oscillating device-notshown so that the guide roller 44 may be oscillated during thedeveloping operation, thereby facilitating the continuous and smoothcascade of the developer 40 upon the recording medium 32. The developer40, after development, is mixed by a roller 48 having mixing blades orvanes 48a so that the concentration of the tonner in the developer maybe equalized and directed toward the driving roller 41 forre-circulation. The excess tonner adhered to the recording medium 32 isremoved by a fog preventative brush 49 and returned to the tray 39.

The powder image thus formed upon the recording medium 32 is transferredto a transfer sheet or the like 50 pressed against the recording medium32 by means of a pair of pressure roller 51a and 51b. The sheet 50 maybe advanced by a conveyor means not shown at the same velocity as thatof the recording medium 32. When the sheet 50 is closely pressed againstthe recording medium 32, the powder image thereupon is transferred tothe sheet 50 by the corona discharge ofa charging device 53 electricallyconnected to a high-voltage source 52. The transferred image is heatedand fixed to the sheet 50 by an infra-red lamp 54 having a reflector54a. Thereafter the residual tonner upon the recording medium 32 isremoved by a cleaning brush 55 for preparation of the next operation.The cleaning brush 55 is surrounded by a shielding plate 550 forpreventing the dispersion ofthe tonner.

FIG. 4 is a diagrammatic sectional view of a dry process developingdevice to which is applied the present invention in such a manner that anon-magnetic belt 146 is advanced in closely spaced apart relation withthe recording medium 32 over the developing zone B so as to attain aspecial electrostatic conduction effect for development, thereby furtherimproving the development. More particularly, the non-magnetic belt 146comprises an endless belt made of fabrics or rubber and a thinnon-magnetic metallic sheet such as aluminum, stainless steel, etc.laminated upon the endless belt, and is wrapped over the magnetic belt43 and around a pair of guide rollers 144a and l44b disposedsubstantially at both ends of the developing zone B respectively andadjacent to the rotary drum 31. In order to space the non-magnetic belt146 from the recording medium 32 by about 5 mm, a belt guide plate 147is disposed as shown in FIG. 4. The non-magnetic belt 146 is advancedover the developing zone B along the rotary drum 31 so that the specialelectrostatic conduction effect for development may be attained, therebysubstantially eliminating the edge effect of the developed image. Thenonmagnetic belt 146 may be made only of a non-magnetic metallic sheet.

The present invention has been so far described with particularreference to the illustrative embodiments thereof, but it will beunderstood that variations and modifications can be effected withoutdeparting from the true spirit of the present invention as describedhereinabove and a defined in the appended claims.

What is claimed is:

l. A device for a dry process electrophotographic cascade developmentcomprising a developer sump,

a magnetic endless belt trained around a pair of spaced apart rollermeans,

a non-magnetic endless belt partially wrapped over said magnetic endlessbelt along its going pass and trained around a guide roller meansdisposed in spaced apart relation from the upper one of said pair ofroller means and adjacent to the upper end of a development zone of anelectrophotographic recording medium overlaid upon the peripheralsurface of a rotary drum in such a manner that said non-magnetic beltmay be separated from said magnetic belt adjacent to said upper rollermeans, and

drive means for driving at least said non-magnetic endless belt, saidmagnetic endless belt having means for generating the magnetic fieldthrough both of said magnetic and non-magnetic endless belts, wherebythe developer in said sump is entrained upon said non-magnetic endlessbelt and transported to an area adjacent to said guide roller means andthe free movement of said developer upon said non-magnetic endless beltbeing permitted upon said separation of said non-magnetic belt from saidmagnetic belt so that the developer may be freely cascaded over saiddevelopment zone from an area adjacent to said guide roller reans.

2. A device as specified in claim 1 wherein means is provided foroscillating said guide roller means so as to oscillate said non-magneticendless belt when the developer is cascaded.

3. A device as specified in claim 1 wherein mixing means is provided formixing the developer returned from said cascade over said recordingmedium into said developer sump and for directing the developer towardthe lower one of said pair of roller means.

4. A device as specified in claim 2 wherein mixing means is provided formixing the developer returned from said cascade over said recordingmedium into said developer sump and for directing the developer towardthe lower one of said pair of roller means.

5. A device for a dry process electrophotographic cascade developmentcomprising a developer sump,

a magnetic endless belt trained around a pair of spaced apart rollermeans,

a non-magnetic metallic belt partially wrapped over said magneticendless belt along its going pass and trained around a pair of mutuallyspaced apart guide roller means disposed substantially at both ends of adevelopment zone of a recording medium overlaid upon the peripheralsurface of a rotary drum in such a manner that said non-magneticmetallic belt may be separated from said magnetic belt adjacent to theupper one of said pair of roller means and pass along said developmentzone in closely spaced apart relation therewith,

a guide plate means for ensuring said pass of said non-magnetic metallicbelt along said development zone in closely spaced apart relationtherewith, and

drive means for driving at least said non-magnetic metallic belt,

mixing means for mixing the developer returned into said developer sumpfrom said recording medium and for directing the developer toward thelower one of said pair of roller means,

said magnetic endless belt having means for generating the magneticfield through both of said magnetic and nonmagnetic metallic endlessbelts, whereby the developer in said sump is entrained upon saidnon-magnetic endless belt and transported to an area adjacent to theupper one of said pair of mutually spaced apart guide roller means, and

1. A device for a dry process electrophotographic cascade developmentcomprising a developer sump, a magnetic endless belt trained around apair of spaced apart roller means, a non-magnetic endless belt partiallywrapped over said magnetic endless belt along its going pass and trainedaround a guide roller means disposed in spaced apart relation from theupper one of said pair of roller means and adjacent to the upper end ofa development zone of an electrophotographic recording medium overlaidupon the peripheral surface of a rotary drum in such a manner that saidnon-magnetic belt may be separated from said magnetic belt adjacent tosaid upper roller means, and drive means for driving at least saidnon-magnetic endless belt, said magnetic endless belt having means forgenerating the magnetic field through both of said magnetic andnon-magnetic endless belts, whereby the developer in said sump isentrained upon said non-magnetic endless belt and transported to an areaadjacent to said guide roller means and the free movement of saiddeveloper upon said non-magnetic endless belt being permitted upon saidseparation of said non-magnetic belt from said magnetic belt so that thedeveloper may be freely cascaded over said development zone from an areaadjacent to said guide roller reans.
 2. A device as specified in claim 1wherein means is provided for oscillating said guide roller means so asto oscillate said non-magnetic endless belt when the developer iscascaded.
 3. A device as specified in claim 1 wherein mixing means isprovided for mixing the developer returned from said cascade over saidrecording medium into said developer sump and for directinG thedeveloper toward the lower one of said pair of roller means.
 4. A deviceas specified in claim 2 wherein mixing means is provided for mixing thedeveloper returned from said cascade over said recording medium intosaid developer sump and for directing the developer toward the lower oneof said pair of roller means.
 5. A device for a dry processelectrophotographic cascade development comprising a developer sump, amagnetic endless belt trained around a pair of spaced apart rollermeans, a non-magnetic metallic belt partially wrapped over said magneticendless belt along its going pass and trained around a pair of mutuallyspaced apart guide roller means disposed substantially at both ends of adevelopment zone of a recording medium overlaid upon the peripheralsurface of a rotary drum in such a manner that said non-magneticmetallic belt may be separated from said magnetic belt adjacent to theupper one of said pair of roller means and pass along said developmentzone in closely spaced apart relation therewith, a guide plate means forensuring said pass of said non-magnetic metallic belt along saiddevelopment zone in closely spaced apart relation therewith, and drivemeans for driving at least said non-magnetic metallic belt, mixing meansfor mixing the developer returned into said developer sump from saidrecording medium and for directing the developer toward the lower one ofsaid pair of roller means, said magnetic endless belt having means forgenerating the magnetic field through both of said magnetic andnon-magnetic metallic endless belts, whereby the developer in said sumpis entrained upon said non-magnetic endless belt and transported to anarea adjacent to the upper one of said pair of mutually spaced apartguide roller means, and the free movement of said developer upon saidnon-magnetic metallic endless belt being permitted when saidnon-magnetic metallic endless belt is separated from said magneticendless belt so that the developer may be freely cascaded over saiddevelopment zone from an area adjacent to the upper one of said pair ofguide roller means.
 6. A device as specified in claim 1 wherein saidnon-magnetic metallic endless belt comprises an endless belt made offabrics or rubber with a thin non-magnetic metallic sheet laminatedthereover.